Substrate free ultrasonic-assisted hydrothermal growth of ZnO nanoflowers at low temperature

Synthesis and performance evaluation of zinc oxide tubes/alginate microfibre composites for photodegradation of methylene blue: a novel reporting approach

This research investigates the efficacy of zinc oxide (ZnO) tubes in decontaminating polluted water using a substrate-free hydrothermal synthesis process for ZnO tubes. The synthesized tubes are impregnated into calcium alginate microfibres, strategically chosen for their high surface area to enhance photocatalytic degradation performance and for practical handling during decontamination and subsequent collection, thereby preventing secondary contamination. Structural and morphological analyses, conducted using Scanning Electron Microscopy (SEM) and X-ray Diffraction (XRD), thoroughly characterize the properties of the ZnO tubes and the composite material. The efficacy of this composite is demonstrated through the photocatalytic degradation of methylene blue (MB), as a representative organic pollutant, resulting in an 88% degradation of MB after 5 hours of irradiation by a sun simulator. Cyclic tests exhibit consistent degradation levels in the first four cycles (81-89%), followed by a subsequent decrease to 72% in the fifth cycle, coinciding with the breakdown of the microfibres into shorter fragments. Innovatively, this study introduces an approach to reporting photocatalytic degradation results, utilizing normalized pollutant concentration plotted against irradiated energy instead of time, as energy encompasses irradiated power, time, and surface area. This reveals that the 88% degradation of MB is achieved by irradiating the sample with an approximately 18 kJ. Additionally, a new metric, Specific Energy Efficiency (SEE), is introduced. It expresses the ratio of degraded pollutant mass to the mass of photocatalytic active material per unit of irradiated energy, with the maximum and cumulative SEE in this study being 1.044 μg g-1 J-1 and 326 ng g-1 J-1, respectively. This research not only contributes to the understanding of ZnO tubes' efficiency in polluted water decontamination but also introduces valuable insights for standardized reporting in photocatalytic degradation studies.

Bicone nanoflower evolution and multi-peak emission of polymer caped Cu doped ZnO

A low-temperature polymer-assisted wet chemical method was used to synthesise Cu-doped ZnO bicone nanoflowers at three different polyethylene glycol (PEG) concentrations. The effects of PEG concentration on the structural, morphological and optical properties of Cu doped ZnO nanostructures were studied. X-ray diffraction studies revealed that the as-synthesized Cu doped ZnO nanostructures are highly crystalline with a hexagonal wurtzite phase. The scanning electron microscopy analysis showed that the prepared nanostructures have bicone- nanoflower morphology and PEG concentration has strongly influenced the size as well the shape of nanoflowers. The TEM analysis confirmed the nanoflower morphology and the presence of diffraction planes obtained from the XRD data. The compositional analysis was performed by x-ray photoelectron Spectroscopy. The surface passivation effect of PEG on the band gap energies was studied by analysing UV -visible spectra of all the samples. The room-temperature fluorescent spectra of all the nanoflowers showed multiple peak emissions, both in the ultra-violet and visible regions, with varying intensities. These recasted multiple peaks are attributed to the morphological modification caused by the PEG addition.

Enhanced Visible-Light Photodetection with Undoped and Doped ZnO Thin-Film Self-Powered Photodetectors

Photodetection plays an essential role in the visible-light zone and is important in modern science and technology owing to its potential applications in various fields. Fabrication of a stable photodetector remains a challenge for researchers. We demonstrated a high-response/recovery and self-powered undoped ZnO (UZO) and Cu-doped ZnO (CZO) thin film-based visible-light photodetector fabricated on a cost-effective Si substrate using reactive cosputtering. The structural, morphological, and optical properties of CZO and UZO thin films have been examined using X-ray diffraction, field emission scanning electron microscopy, X-ray photoelectron spectroscopy, atomic force microscopy, and photoluminescence spectroscopy. The results of the CZO/n-Si photodetector compared with those of the undoped ZnO (UZO)/n-Si photodetector show that the CZO/n-Si exhibits a higher on/off ratio, responsivity, and detectivity than UZO/n-Si. Also, the CZO/n-Si photodetector shows high stability and reproducibility over 20 cycles after 180 days. A relative study of CZO/n-Si- and UZO/n-Si-based photodetectors reveals the enhanced performance of the CZO/n-Si photodetector, which has a high on/off ratio of ∼300 with a high specific detectivity of 2.8 × 1010 Jones for 75 mW visible light. The prepared self-powered CZO/n-Si/Ag thin film-based visible-light photodetector paves the way for the development of high-performance photodetector designs.

Investigations of a Statistical and Analytical Method to Find the Relationship between the Morphological and Optical Properties of ZnO Nanoflower Arrays

In this study, a sapphire substrate with a patterned concave structure was used to prepare ZnO film/A-B glue, and the ZnO film/A-B glue with a patterned convex matrix was transferred onto a silicon wafer using the lift-off technology as the seed layer. Then, the hydrothermal method with different Zn(CH₃COO)₂ and C₆H₁₂N₄ concentrations as precursors was used to synthesize ZnO nanoflower arrays on the patterned convex ZnO seed layer. XRD pattern, FESEM, FIB, and photoluminescence (PL) spectrometry were employed to observe and analyze the properties of the synthesized ZnO nanoflower arrays. When Zn(CH₃COO)₂ and C₆H₁₂N₄ concentrations were 0.01, 0.02, 0.03, and 0.04 M, the average heights of the ZnO nanorods in the ZnO nanoflower arrays were 993, 1500, 1550, and 1650 nm, the average diameters of the ZnO nanorods were 50, 90, 105, and 225 nm, and the aspect ratios (H/D) of the ZnO nanorods were 19.9, 16.7, 14.8, and 7.33, respectively. A simple statistical and analytical method was investigated to estimate the densities (number of nanorods) of the ZnO nanoflower arrays in one 1 μm × 1 μm area. The total surface area (S) of the ZnO nanoflower arrays first increased from 5.05 × 10⁶ and then reached a maximum value of 1.20 × 10⁷ nm² as Zn(CH₃COO)₂ and C₆H₁₂N₄ concentrations increased from 0.01 to 0.02 M. For the systhesized ZnO nanoflower arrays, as the Zn(CH₃COO)₂ and C₆H₁₂N₄ concentrations increased from 0.01 to 0.04 M, their total volume (V) increased from the 6.23 × 10⁷ to 5.90 × 10⁸ nm³ and the S/V ratio decreased from 8.10 × 10^-2 to 1.84 × 10^-2. We found that ZnO nanoflower arrays with Zn(CH₃COO)₂ and C₆H₁₂N₄ concentrations of 0.2 M presented the maximum PL emission intensities. The calculated S/V ratios and X-ray photoelectron spectroscopy analyses are used to discuss the reasons for these results.

Application of Zinc Oxide nanoflowers in Environmental and Biomedical Science

Zinc oxide (ZnO) nanostructures can be synthesized in nanoforms of spheres, rods, flowers, disks, walls, etc., among which nanoflowers have gained special attention due to their versatile biomedical and pollutant remedial applications in waste water and air. ZnO nanoflowers have an ultrasmall size with a huge surface area to volume ratio due to their hexagonal petal structures which render them superior compared to the nanoparticles of other shapes. The ZnO nanoflowers have bandgap energy equivalent to a semiconductor that makes them have unique photophysical properties. We have used the appropriate keywords in Google Scholar and PubMed to obtain the recent publications related to our topic. We have selected the relevant papers and utilized them to write this review. The different methods of synthesis of ZnO nanoflowers are chemical vapor deposition, facile hydrothermal, thermal evaporation, chemical reduction, bio route of synthesis, and solvothermal method, etc. which are mentioned in this review. ZnO nanoparticles are used in paints, cosmetics, and other products due to their high photocatalytic activity. The different applications of ZnO nanoflowers in the diagnosis of disease biomarkers, biosensors, catalysts, and the therapeutic process along with wastewater remediation and gas sensing applications will be discussed in this review.

A Novel Synthesis of ZnO Nanoflower Arrays Using a Lift-Off Technique with Different Thicknesses of Al Sacrificial Layers on a Patterned Sapphire Substrate

A novel method to synthesize large-scale ZnO nanoflower arrays using a protrusion patterned ZnO seed layer was investigated. Different thicknesses of aluminum (Al) film were deposited on the concave patterned sapphire substrate as a sacrificial layer. ZnO gel was layered onto the Al film as a seed layer and OE-6370HF AB optical glue was used as the adhesive material. A lift-off technique was used to transfer the protrusion patterned ZnO/AB glue seed layer to a P-type Si <100> wafer. The hydrothermal method using Zn(CH₃COO)₂ and C₆H₁₂N₄ solutions as liquid precursors was used to synthesize ZnO nanoflower arrays on the patterned seed layer. X-ray diffraction spectra, field-effect scanning electron microscopy, focused ion beam milling (for obtaining cross-sectional views), and photoluminescence (PL) spectrometry were used to analyze the effects that different synthesis times and different thicknesses of Al sacrificial layer had on the properties of ZnO nanoflower arrays. These effects included an increased diameter, and a decreased height, density (i.e., number of nanorods in μm⁻²), total surface area, total volume, and maximum emission intensity of PL spectrum. We showed that when the synthesis time and the thickness of the Al sacrificial layer were increased, the emission intensities of the ultraviolet light and visible light had different variations.

CuZn and ZnO Nanoflowers as Nano-Fungicides against Botrytis cinerea and Sclerotinia sclerotiorum: Phytoprotection, Translocation, and Impact after Foliar Application

Inorganic nanoparticles (INPs) have dynamically emerged in plant protection. The uptake of INPs by plants mostly depends on the size, chemical composition, morphology, and the type of coating on their surface. Herein, hybrid ensembles of glycol-coated bimetallic CuZn and ZnO nanoparticles (NPs) have been solvothermally synthesized in the presence of DEG and PEG, physicochemically characterized, and tested as nano-fungicides. Particularly, nanoflowers (NFs) of CuZn@DEG and ZnO@PEG have been isolated with crystallite sizes 40 and 15 nm, respectively. Organic coating DEG and PEG (23% and 63%, respectively) was found to protect the NFs formation effectively. The CuZn@DEG and ZnO@PEG NFs revealed a growth inhibition of phytopathogenic fungi Botrytis cinerea and Sclerotinia sclerotiorum in a dose-dependent manner with CuZn@DEG NFs being more efficient against both fungi with EC50 values of 418 and 311 μg/mL respectively. Lettuce (Lactuca sativa) plants inoculated with S. sclerotiorum were treated with the NFs, and their antifungal effect was evaluated based on a disease index. Plants sprayed with ZnO@PEG NFs showed a relatively higher net photosynthetic (4.70 μmol CO2 m-2s-1) and quantum yield rate (0.72) than with CuZn@DEG NFs (3.00 μmol CO2 m-2s-1 and 0.68). Furthermore, the penetration of Alizarin Red S-labeled NFs in plants was investigated. The translocation from leaves to roots through the stem was evident, while ZnO@PEG NFs were mainly trapped on the leaves. In all cases, no phytotoxicity was observed in the lettuce plants after treatment with the NFs.